Four types of next generation batteries are currently being envisaged among the international community: lithium-sulfur, metal-air, and metal-sodium batteries, multivalent cation batteries and all-solid-state battery concepts (M. Tatsumisago and Hayashi, A. Sol. Stat. Ionics, 2012, 225, 342). These battery designs require high-performance, safe and cost effective electrolytes that are compatible with optimized electrode materials. Solid electrolytes have not yet been extensively employed in commercial batteries as they suffer poor ionic conduction at acceptable temperatures and insufficient stability with respect to lithium-metal.
Chen and co-workers (Z. Chen, Y. Qini, Y. Ren, W. Lu, C. Orendorff, E. P. Roth and K. Amine, Energy Environ. Sci. 2011, 4, 4023) showed that higher graphite negative electrode surface area in a lithium-ion cell can result in more solid electrolyte interphase (SEI) and therefore more heat generation during thermal decomposition. This initial reaction, which occurs at ˜110° C., can further trigger other exothermal reactions in the cell. Therefore, the latest work on graphitic anodes mainly focuses on the development of a stable artificial solid electrolyte interphase to stabilize the lithiated graphite and improve both safety and cycling performance.
Recently, lithium batteries using oxygen from air at the positive electrode (lithium-air batteries) have attracted world-wide attention. In this open system, the use of electrolytes with low volatility is strictly required. For the lithium-air batteries a major focus of attention has been the lithium-metal anode protected by a lithium-ion conducting ceramic electrolyte (N.-S. Choi, Z. Chen, S. A. Freunberger, X. Ji, Y.-K. Sun, K. Amine, G. Yushin, L. F. Nazar, J. Cho and P. G. Bruce, Angew. Chem. Int. 2012, 51, 9994). LISICON (Li(1+x+y)AlxTi2−xSiyP(3−y)O12) (Ohara Inc. 2013) has been used for the previous purpose with a major inconvenient related to—LISICON being reduced in contact with Li-metal—following-on a Li/ceramic interface difficult to cycle (N.-S. Choi, Z. Chen, S. A. Freunberger, X. Ji, Y.-K. Sun, K. Amine, G. Yushin, L. F. Nazar, J. Cho and P. G. Bruce, Angew. Chem. Int. 2012, 51, 9994).
Promising results were recently obtained with a Li10GeP2S12 solid electrolyte N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y. Kato, S. Hama, K. Kawamoto and A. A. Mitsui, Nature Mat. 2011, 10, 682). In this solid electrolyte medium, Li+ ions are conducted at 0.012 mScm−1 and 12 mScm−1 at −100° C. and 25° C., respectively, which is considered to be a high conductivity. Mo et al (Y. Mo, S. P. Ong and G. Ceder, Chem. Mater. 2012, 24, 15) found that Li10GeP2S12 is not stable against reduction by lithium at low voltage or extraction of Li with decomposition at high voltage.
On a different front, sulfide glasses have been studied due to their high ionic conductivity. A glass of the Li3PO4—Li2S—SiS2 system is formed at ambient pressure by quenching 0.03Li3PO4-0.59Li2S-0.385Si2 in liquid nitrogen. Its conductivity at room temperature is 0.69 mScm−1 (S. Kondo, K. Takada and Y. Yamamura, Sol. Stat. Ionics 1992, 53-56(2), 1183) and its stability against electrochemical reduction is as wide as 10 V (A. Hayashi, H. Yamashita, M. Tatsumisago and T. Minami, Sol. Stat. Ionics 2002, 148, 381).
On the other hand, for lithium-ion or sodium-ion electrochemical devices such as capacitors and especially batteries, the safety issue remains a major barrier. Battery manufacturers are now able to produce high-quality lithium-ion cells for consumer electronics, with less than one reported safety incident for every one million cells produced. However, this failure rate is still too high for applications in plug-in hybrid electric vehicles and pure electric vehicles, since several hundred of lithium-ion cells will be needed to power a vehicle. The failure of a single cell can generate a large amount of heat and flame, both of which can then trigger thermal runaway of neighbouring cells, leading to failure throughout the battery pack. Consequently, there is a wide effort to tackle the safety issue of lithium batteries.
Typically, the conductivity of liquid state of the art electrolytes at room temperature (20° C.) is about 10 mScm−1, and it increases by approximately 30-40% at 40° C. The electrochemical window of stability of liquid electrolytes is usually equal or smaller than 4 V, not enabling their use with all the pairs of electrodes.
The stability of the electrolyte is related to its electrochemical window which is directly related with the electrical band gap. The calculated electronic energy band gap for Li3ClO crystalline solid is 6.44 eV and does not change more than the decimal value of an eV with low dopant levels up to 0.7 at %. Cyclic voltammetry experiments conducted to determine the window of stability of the glassy samples at 130° C. have shown a stability range of more than 8 V, which allows the application of our electrolyte in next generation high voltage battery cells (5 V).
These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.
General Description
The present disclosure relies on a novel type of glasses, which is a disordered amorphous phase presenting a glass transition and showing the highest ionic conductivity of at least 13 mScm−1 at 25° C. for Li-ion and at least 17 mScm−1 for Na-ion at 25° C. These glassy electrolytes for lithium/sodium batteries are inexpensive, light, recyclable, non-flammable and non-toxic. Moreover, they present a wide electrochemical window (higher than 8 V) and thermal stability within the application range of temperatures.
A lithium-ion or sodium-ion battery is a rechargeable type of battery, wherein lithium/sodium ions move, through the electrolyte, from the negative electrode to the positive electrode during the discharge process and back during the charging process. The battery's electrochemistry is governed by an overall reaction occurring at the positive and negative electrodes and the battery's maximum open circuit potential difference is determined by the cited reaction.
A lithium-ion or sodium-ion electrical double layer capacitor (EDLC) is a supercapacitor, wherein lithium/sodium ions move, through the electrolyte towards the negative electrode accumulating at the interface and forming a nanometric spaced capacitor with the electrode's negative ions or electrons during charge. At the opposite interface, electrode's positive ions form another EDLC with the negative ions of the electrolyte (which are negative due to lack of Li or Na cations). The capacitor's operating potential difference is determined by the electrolyte's electrochemical window of stability.
The lithium-ion or sodium-ion batteries and capacitors are lightweight, high energy density power sources for a variety of devices, such as portable devices, power tools, electric vehicles, and electrical grid storage; contain no toxic metals and are therefore characterized as non-hazardous waste.
The disclosed subject-matter relates to a glassy electrolyte for Li-ion or Na-ion (Li+ and Na+, respectively). The glass is synthesized from a compound with stoichiometry R3-2xMxHalO, wherein R is lithium (Li) or sodium (Na); M is magnesium (Mg), calcium (Ca), strontium (Sr), or barium (Ba); Hal is fluorine (F), chlorine (Cl), bromine (Br) or iodine (I), or a mixture between these elements; O is oxygen. Furthermore, 0≤x≤0.01, preferably with 0.002≤x≤0.007; preferably with 0.003≤x≤0.005.
The glassy electrolyte, after reaching the vitreous state, is a Li+ ion or Na+ ion superconductor in addition to being an electrical insulator demonstrating the essential functional characteristics of an electrolyte. The ionic conductivity in the disclose glassy electrolyte, comprising Li+ ion or Na+ ion, improves at least two orders of magnitude comparing with the crystalline material. The electrochemical window becomes also wider from 6 V to more than 8 V. It can, therefore, be applied between the negative and positive electrodes of a lithium battery or capacitor if R in the formula of the compound mentioned above is lithium, or to a sodium battery or capacitor if R in the same formula is sodium.
This glass has proved to be anti-flammable, to have lightweight, being recyclable, easy to synthesize and of low cost.
An embodiment of the disclosed subject-matter is relate to solid electrolyte glass comprising formula R3-2xMxHalO wherein                R is selected from the group consisting of lithium or sodium;        M is selected from the group consisting of magnesium, calcium, strontium or barium;        Hal is selected from the group consisting of fluorine, chlorine, bromine, iodine or mixtures thereof;        X is the number of moles of M and 0≤x≤0.01;        and the solid electrolyte glass has a glass transition point.        
In an embodiment the solid electrolyte glass does not have a peak with a half-value width of 0.64° or less in a range of 31°≤2θ≤34° in measurement by an X-ray diffraction method using a CuKα ray.
In an embodiment the Li3-2x0.005Ba0.005ClO glassy electrolyte does not have a peak with a half-value width of 0.64° or less in a range of 31°≤2θ≤34° in measurement by an X-ray diffraction method using a CuKα ray.
In an embodiment the solid electrolyte glass of the present disclosure has a ionic conductivity of at least 13 mScm−1 at 25° C. wherein R is a ion lithium; preferably an ionic conductivity of 13-60 mScm−1 at 25° C., more preferably an ionic conductivity of at least 25 mScm−1 at 25° C.
In an embodiment the solid electrolyte glass of the present disclosure has a ionic conductivity of at least 17 mScm−1 at 25° C. wherein R is a ion sodium; preferably an ionic conductivity of 17-105 mScm−1 at 25° C., more preferably an ionic conductivity of at least 31 mScm−1 at 25° C.
The ionic conductivity can be measured by standard methods, namely by Electrochemical Impedance Spectroscopy (EIS) at 25° C.
In an embodiment the solid electrolyte glass of the present disclosure X in the formula may be 0.002, 0.005, 0.007 or 0.01.
In an embodiment the solid electrolyte glass of the present disclosure Hal may be a mixture of chloride and iodine.
In an embodiment the solid electrolyte glass of the present disclosure Hal may be Hal=0.5Cl+0.51.
In an embodiment the solid electrolyte glass of the present disclosure wherein R is lithium:    M is barium, Hal is chlorine and x is 0.005 or;    M is barium, Hal is a mixture of chlorine and iodine, x is 0.005.
In an embodiment the solid electrolyte glass of the present disclosure wherein R is sodium, M is Ba, Hal is Cl and x is 0.005.
Another aspect of the present disclosure is related to a electrolyte composition, in particular a solid electrolyte glass composition, of the formula Na3-2xMxHalO wherein                M is selected from the group consisting of magnesium, calcium, strontium or barium;        Hal is selected from the group consisting of fluorine, chlorine, bromine, iodine or mixtures thereof;        X is the number of moles of M and 0<x≤0.01.        
Another aspect of the present disclosure is related to an electrochemical device comprising a glassy electrolyte describes in the present disclosure.
Another aspect of the present disclosure is related to a battery comprising a glassy electrolyte describes in the present disclosure.
Another aspect of the present disclosure is related to a capacitor comprising the glassy electrolyte describes in the present disclosure.
Another aspect of the present disclosure is related to an electrochemical device comprising at least one capacitor of the present describes in the present disclosure and at least one battery describes in the present disclosure.
Another aspect of the present disclosure is related to a method for synthetizing a conductive glass electrolyte, in particular for preparing 5 g, comprising a compound of the formula R3-2xMxHalO wherein                R is lithium;        M is selected from the group consisting of magnesium, calcium, strontium or barium;        Hal is selected from the group consisting of fluorine, chlorine, bromine, iodine or mixtures thereof, in particular Cl;        X is the number of moles of M and 0≤x≤0.01;        comprising the following steps:        mixing a stoichiometric quantity of LiHal, LiOH, and one of the following compounds: Mg(OH)2; Ca(OH)2, Sr(OH)2 or Ba(OH)2;        adding to said mixture deionized water and mixing to form a solution in a closed container;        heating said solution up to 250° C. during 2-8 h;        opening the container to evaporate the excess of water in the heated product.        
In one embodiment, the method for synthetizing any of the compounds of the previous paragraph may comprise the following step:                introducing the synthetized glassy material between electrodes the electrodes of an electrochemical device;        heating the glassy material up to 170-240° C. and cooling.        
In one embodiment, the method for synthetizing any of the compounds of the previous paragraph may comprise the following step:                a stoichiometry mixture of LiCl, LiOH, and one of the following compounds:        Mg(OH)2; Ca(OH)2, Sr(OH)2 or Ba(OH)2, is used; the mixture is introduced in a Teflon reactor with 1-2 drops of deionized water and mixing to form a homogenous paste which is kept closed in the reactor and introduced in a sand bath;        the mixture is heated up to 250° C. and kept for at least 4 h;        the reactor is opened to let the excess of water evaporate;        a glass material synthetized is introduced between two gold square electrodes with 1 cm wide and pressed with the aid of a clip for the electrolyte to gain a regular thickness equal to 1-3 mm;        the glass material produced is heated up to 230° C. and cooled down in the sand bath, 2-5 times under the action of a variable potential difference between −10 V and 10 V with variable frequencies between 100 Hz and 5 MHz.        
Another aspect of the present disclosure is related to a method for synthetizing a conductive glass electrolyte, in particular for preparing 5 g, comprising a compound of the formula R3-2xMxHalO wherein                R is sodium;        M is selected from the group consisting of magnesium, calcium, strontium and barium;        Hal is selected from the group consisting of fluorine, chlorine, bromine, iodine or mixtures thereof;        X is the number of moles of M and 0≤x≤0.01 of        comprising the following steps:        mixing a stoichiometry quantity of NaHal, NaOH and one of the following compounds: Mg(OH)2; Ca(OH)2; Sr(OH)2 or Ba(OH)2;        adding to said mixture deionized water and mixing to form a solution in a closed container;        heating the solution up to 70-90° C. for 2-8 h;        increasing the temperature up to 190-250° C. for 2-8 h, maintaining said temperature for at least 2 h;        opening the container to evaporate the excess water in the heated product.        
In one embodiment, the method for synthetizing any of the compounds of the previous paragraph may comprise the following step:                introducing the synthetized glass material between electrodes; heating the glass up to 190-230° C. and cooling.        
In one embodiment, the method for synthetizing any of the compounds of the previous paragraph may comprise the following step:                a stoichiometry mixture of NaCl, NaOH and one of the following compounds:        Mg(OH)2; Ca(OH)2; Sr(OH)2 or Ba(OH)2 or        a stoichiometry mixture of NaCl, NaF, NaOH and one of the following compounds: Mg(OH)2; Ca(OH)2; Sr(OH)2 or Ba(OH)2 is used;        the mixture is introduced in a reactor with 1-2 drops of deionized water and mixed to form a homogenous paste which is kept closed in the reactor and introduced in a sand bath;        the mixture is heated up to 80° C. for 2 h;        the temperature is increased to 120° C. for 24 h;        the temperature is increased to 245° C. for 24 h;        the temperature is maintained for at least 4 h;        the reactor is opened to let the excess of water evaporate;        a glassy material synthetized is introduced between two gold square electrodes with 1 cm wide and pressed with the aid of a clip for the electrolyte to gain a regular thickness equal to 1-3 mm;        the glass material produced is heated up to 230° C. and cooled down in the sand bath;        the glass material is heated up to 140° C. and cooled down in the sand bath 2-5 times under the action of a variable potential difference between −10 V and 10 V with variable frequencies between 100 Hz and 5 MHz.        
Another aspect of the present disclosure is related to a method for synthetizing a ion conductive glassy electrolyte, in particular for preparing 5 g, comprising a compound of the formula R3-2xMxHalO wherein                R is lithium;        M is selected from the group consisting of magnesium, calcium, strontium or barium;        Hal is selected from the group consisting of fluorine, chlorine, bromine, iodine or mixtures thereof;        X is the number of moles of M and 0≤x≤0.01 of        comprising the following steps:        mixing a stoichiometry quantity of LiCl, LiOH and one of the following compounds: Mg(OH)2; Ca(OH)2; Sr(OH)2 or Ba(OH)2;        adding to said mixture deionized water, in particular 5-25 ml or 1-2 drops, and mixed to form a solution, in particular an homogeneous paste, in a closed container;        heating said solution up to 250° C. during 2-8 h;        opening the container to evaporate the excess of water in the product;        introducing the glass material synthetized between the electrodes, in particular a glass material synthetized is introduced between two gold square electrodes with 1 cm wide and pressed with the aid of a clip for the electrolyte to gain a regular thickness equal to 1-3 mm;        the glass obtained is heated up to 170-240° C. and cooled down, in particular 2-5 times under the action of a variable potential difference between −10 V and 10 V with variable frequencies between 100 Hz and 5 MHz.        
Another aspect of the present disclosure is related to the use of the composition of the formula R3-2xMxHalO wherein                R is selected from the group consisting of lithium or sodium;        M is selected from the group consisting of magnesium, calcium, barium or strontium;        Hal is selected from the group consisting of fluorine, chlorine, bromine, iodine or mixtures thereof;        X is the number of moles of M and 0≤x≤0.01;as an enhancer of the ionic conductivity of an electrolyte and/or of the electrochemical window of stability of an electrolyte.        
The disclosed subject matter relates to a glassy electrolyte optimized with ultra-fast ionic conduction based on an R3-2xMxHalO stoichiometry, in which R is lithium or sodium ion, M is a higher valent cation such as Mg2+, Ca2+, Sr2+, Ba2+; and Hal is a halide anion like F−, Cl−, Br− or I− or a mixture of halides anions.
The glass-liquid transition is the reversible transition in amorphous materials from a hard and relatively brittle state into a molten or rubber-like state. The glass transition of a liquid to a solid-like state may occur with either cooling or compression. The transition comprises a relatively smooth increase in the viscosity of a material of about 17 orders of magnitude without any pronounced change in material structure. The consequence of this dramatic increase is a glass exhibiting solid-like mechanical properties on the timescale of practical observation. While glasses are often thought of as rigid and completely immobile, it is well known that relaxation processes of one type or another continue to be measurable all the way down to the cryogenic range. Hundreds of degrees below Tg, on the other hand, there is frequently an important source of dielectric loss in ordinary glass insulators. This is attributed to mobile alkali ions and, to a lesser extent, protons, in the anionic network. In many cases, for example in solid electrolytes, these quasi-free modes of motion are the focus of special materials interest such as advanced solid electrolytes based on freely mobile cations.
A more operative classification for the glass transition temperature is that at this temperature—or within a few degrees up to for example 50° C.—the specific heat, the coefficient of thermal expansion and eventually the dielectric constant change abruptly. In the Differential Scanning calorimetry (DSC) experiment, Tg is expressed by a change in the base line, indicating a change in the heat capacity of the material. Usually, no enthalpy (latent heat change) is associated with this transition (it is a second order transition); therefore, the effect in a DSC curve is slender and is distinguishable only if the instrument is sensitive.
These solid electrolytes undergo a viscous liquid to a solid-like transition, at Tg. Above Tg a non-Arrhenius conductivity regime is observed [Tg(Li3ClO)≈119° C., Tg(Li3-2*0.005Mg0.005ClO)≈109° C., Tg (Li3-2*0.005Ca0.005ClO)≈99° C., Tg(Li3-2*0.005Ba0.005ClO)≈75° C., Tg (Li3-2*0.005Ba0.005Cl0.5I0.5O)≈38° C]. One variant of the solid electrolyte developed by us, Li3-2xBaxClO (x=0.005), has a conductivity of 25 mScm−1, 38 mScm−1 and 240 mScm−1 at 25° C., 75° C. and 100° C., respectively, in the glassy state or supercooled liquid state. Another variant, Li3-2xBaxCl0.5I0.5O (x=0.005), has a conductivity of 121 mScm−1 at 50° C. in the supercooled liquid state.
Antiperovskite hydroxides, most of them following the general formula Li3-n(OHn)Hal or Li4(OH)3Cl present ionic conductivities which are surprisingly smaller than the Li3-2*xMxHalO vitreous electrolytes, achieving the highest ionic conductivity, 0.010 Scm−1, at 250° C. (for Li5(OH)3Cl2). Nevertheless, they are observed in our samples prior to the formation of the glasses and they may have an surprisingly important role in glass formation since the translational symmetry characteristic of a homogeneous fluid is broken by exposure to an external force field, in the vicinity of a confining surface (which may be regarded as the source of an external field), or in the presence of an interface between coexisting phases.